A flow control valve is well known, wherein said valve provided with an actuator of a rotary solenoid types, wherein the degree of rotation of a shaft is in proportion to an electric current applied thereto. In this type of solenoid motor, which has been recently developed, a hollow shaft is rotatably supported on a housing. A torsion bar, such as a stainless steel wire, passes through the hollow shaft. The torsion bar has a first end connected to the body adjacent to one end of the hollow shaft and a second end connected to the other end of the hollow shaft. An electro-magnetic force is generated in the hollow shaft for rotating the shaft against the torsional spring force in the torsional bar. Thus, the angular position of the shaft is controlled by changing the electro-magnetic force, so that the degree of the opening of a valve unit connected to the shaft can be controlled.
In the known rotary type of solenoid, the ends of the torsion bar are provided with split sleeves of a tapered shape for fixing the ends of the torsion bar. Each of the ends of the torsion bar is inserted to one end of the shaft or the housing, respectively, so that each sleeve effects fixation of the corresponding end of the torsion bar under a wedge action. However, the prior art connection suffers from a drawback in that it is difficult to maintain the desired effective length of the bar, so that a variation of such length is apt to occur between the valve devices. Due to the variation of the length of the torsion bar, a variation in the spring coefficient is generated, so that a single flow characteristic is not maintained between the valve devices.